The invention relates to gates in general, and more particularly to improvements in gates of the type known as cell wheels or Rotary feeders (hereinafter called rotary feeders).
A rotary feeder comprises a housing having an inlet and an outlet spaced apart from and connected to the inlet by an internal chamber, particularly a cylindrical chamber. The chamber receives a rotor including a shaft which is rotatably journalled in the housing and carries two spaced-apart end walls as well as a plurality of radially extending vanes or blades between the end walls. When the shaft is driven, either by a motor or by a flowable material which is admitted at the inlet, batches of flowable material are caused to advance in the cells or compartments between neighboring vanes and are discharged through the outlet. The peripheral surfaces of the end walls can sealingly engage the adjacent portions of the internal surface of the housing to thus confine the batches of material to advancement from the inlet, within a portion of the chamber and toward and through the outlet. It is also known to provide the internal surface of the housing with annular grooves which are outwardly adjacent the peripheral surfaces of the end walls and receive seals serving to engage the respective peripheral surfaces and to thus enhance the sealing action between the end walls and the housing.
In many instances, a rotary feeder of the above outlined character will be utilized to transport batches of flowable solid material from a first space at the inlet of the housing to a second space at the outlet of the housing. The pressure in the first space can be less, e.g., considerably less, than the pressure in the second space. Such situation can develop when the rotary feeder is installed in a pneumatic conveyor system, and it is normally desirable to ensure that pressurized fluid (such as air or another gaseous fluid) cannot flow from the second space (e.g., a plenum chamber) back toward the first space, e.g., a suction chamber or a chamber wherein the pressure does not or need not appreciably exceed atmospheric pressure. Since the conveying of batches of flowable material from the inlet to the outlet involves angular movement of the rotor relative to the housing, the extent of leakage of pressurized fluid from the outlet toward the inlet depends on the quality of sealing action between the rotor and the housing of the rotary feeder. This creates problems because the rotor must be installed in the housing with at least some (even extremely small) radial play in order to avoid jamming of the rotor shaft and/or of the end walls in the housing. Even slight radial movability of the rotor results in radial displacement of the shaft and of the parts which are mounted on the shaft because such radial displacement is induced by the pressure differential between the outlet and the inlet of the housing. It has been found that a seemingly negligible radial play of the rotor in the housing often results in the establishment of a rather pronounced gap which provides a path for the flow of pressurized gaseous fluid from the higher-pressure space (normally the space in communication with the outlet) toward and into the lower-pressure space (normally the space which communicates with the inlet of the housing). Such paths cannot be readily sealed without unduly increasing friction between the rotor and the housing of a rotary feeder.
European patent application Serial No. 0 462 501 A1 of Waeschle (published Dec. 27, 1991) discloses a rotary feeder wherein a sealing device is installed between the rotor and the housing at one side of the rotor. The inventor proposes to employ a slidable ring which surrounds the shaft of the rotor and is movably installed in a radial internal groove of the housing. A supporting flange is affixed to an end wall of the rotor and carries two O-rings which sealingly engage the housing. If the rotor is caused to perform a radial movement, the flange is caused to temporarily engage the slidable ring and displaces the latter radially in the housing. This is intended to ensure that the sealing action between the rotor and the housing of the cell wheel will remain intact. A drawback of the proposal of Waeschle is that any shifting of the rotor entails the application of a one-sided force to the slidable ring which results in deformation of the ring due to the development of a counter force as a result of friction. The non-uniformly deformed slidable ring causes the development of a non-uniform clearance. Each change of load results in an abrupt impact of the rotor against the slidable ring which, in turn, causes a progressive widening of the gaps and uncontrolled escape of pressurized fluid.
German patent application Serial No. 40 19 627 A1 of Waeschle (published Jan. 9, 1992) discloses a modified rotary feeder with a housing which receives a container having openings at the inlet and at the outlet of the housing. The external surface of the container is surrounded, at least in part, by an elastomeric flange which causes the container to flow in the housing. Such construction is costly and complex and, in addition, still fails to establish a satisfactory sealing action for the end walls of the rotor.